Method, system, and circuit with a driver output interface having a common mode connection coupled to a transistor bulk connection

ABSTRACT

A multi-terminal output with a common mode connection includes an output having a first terminal and a second terminal and having a common mode connection between the first terminal and the second terminal. A bulk connection of a transistor is coupled to the common mode connection. A first set of control signals and a second set of control signals are generated. Each of the first set of control signals has a first rail voltage level associated with a first power domain. The second set of control signals is generated from the first set of control signals. Each of the second set of control signals has a second rail voltage level that is associated with a second power domain. The second power domain is associated with a common mode voltage of outputs of an output driver.

I. FIELD

The present disclosure is generally related to adjusting outputimpedance of a driver.

II. DESCRIPTION OF RELATED ART

Advances in technology have resulted in smaller and more powerfulcomputing devices. For example, there currently exist a variety ofportable personal computing devices, including wireless computingdevices, such as portable wireless telephones, personal digitalassistants (PDAs), and paging devices that are small, lightweight, andeasily carried by users. More specifically, portable wirelesstelephones, such as cellular telephones and internet protocol (IP)telephones, can communicate voice and data packets over wirelessnetworks. Further, many such wireless telephones include other types ofdevices that are incorporated therein. For example, a wireless telephonecan also include a digital still camera, a digital video camera, adigital recorder, and an audio file player. Also, such wirelesstelephones can process executable instructions, including softwareapplications, such as a web browser application, that can be used toaccess the Internet. As such, these wireless telephones can includesignificant computing capabilities.

Such computing devices may include a data or clock transmitter that usesvarious types of components, such as an open-drain output driver. Anopen-drain output driver may be used in some applications that requirehigh speed operations. For example, open-drain output drivers can beused in High-Definition Multimedia Interface (HDMI) complianttransmitters for both clock and data outputs. However, impedancemismatch between an output driver and a transmission line coupled to theoutput driver can impact performance of the transmitter. For example,impedance mismatch may result in lost transmission power due toreflection loss.

III. SUMMARY

An output interface with a common mode connection coupled to atransistor bulk connection is disclosed. The output interface may be anoutput of an open drain driver that provides differential signaling,such as an HDMI driver. The driver may include a resistor network thatis controllable to reduce an impedance mismatch between the driveroutput and transmission lines that may be coupled to the driver output.The resistor network is controlled by transistors, and a bulk connectionof the transistors is coupled to the common mode connection of theoutput interface. When the output interface is coupled to a receiverside that operates at a higher voltage than the output interface, areliability of the transistors may be maintained because of the couplingof the bulk connection of the transistors to the common mode connectionof the output interface. In a particular implementation, when an opendrain driver is coupled to a receiver side that operates at a highervoltage than a driver side supply voltage, a common mode voltage of thedriver output may be utilized to maintain a reliability of one or moredriver side transistors. For example, by coupling the common modevoltage to a bulk connection of a transistor used in adjusting outputimpedance of the open drain driver; the output impedance of the opendrain driver may be adjusted without reducing the reliability of thetransistors.

In a particular embodiment, a circuit includes an output having a firstterminal and a second terminal and having a common mode connectionbetween the first terminal and the second terminal. The circuit alsoincludes at least one transistor having a bulk connection. The bulkconnection is coupled to the common mode connection.

In another particular embodiment, an apparatus includes a resistornetwork including at least one resistor and the apparatus includes afirst set of transistors and a second set of transistors. The first setof transistors is powered by a first power domain. The second set oftransistors is responsive to the first set of transistors. The secondset of transistors is level shifted to a second power domain andcontrols the resistor network.

In a particular embodiment, a method includes generating a first set ofcontrol signals. Each of the first set of control signals has a firstrail voltage level associated with a first power domain. The method alsoincludes generating a second set of control signals from the first setof control signals. Each of the second set of control signals has asecond rail voltage level that is associated with a second power domain.The second power domain is associated with a common mode voltage ofoutputs of an output driver.

One particular advantage provided by at least one of the disclosedembodiments is that output impedance may be adjusted for an open-drainoutput driver that operates at a lower supply voltage than a receiverthat is coupled to the open-drain output driver. Adjusting the outputimpedance of the open-drain driver may enable reduction of impedancemismatch and improve quality of signal transmission.

Other aspects, advantages, and features of the present disclosure willbecome apparent after review of the entire application, including thefollowing sections: Brief Description of the Drawings, DetailedDescription, and the Claims.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a particular illustrative embodiment of amulti-terminal output with a common mode connection;

FIG. 2 is a diagram of a particular embodiment of a system including aparticular illustrative implementation of the multi-terminal output witha common mode connection of FIG. 1;

FIG. 3 is a diagram of a particular illustrative embodiment of aresistor network that may be implemented in the multi-terminal outputwith a common mode connection of FIG. 1 or 2;

FIG. 4 is a diagram of a particular illustrative embodiment of acalibration system that may be implemented in a transmitter thatincludes the multi-terminal output with the common mode connection ofFIG. 1 or the driver of FIG. 2;

FIG. 5 is a diagram of a particular illustrative system that includesmultiple drivers of FIG. 2;

FIG. 6 is a flow chart of a particular illustrative embodiment of amethod of operating the calibration system of FIG. 3 that may be used tocalibrate the multi-terminal output with the common mode connection ofFIG. 1 or the driver of FIG. 2;

FIG. 7 is a block diagram of wireless device including a driver with anadjustable output impedance; and

FIG. 8 is a data flow diagram of a particular illustrative embodiment ofa manufacturing process to manufacture electronic devices that include adriver with an adjustable output impedance.

V. DETAILED DESCRIPTION

Referring to FIG. 1, a particular illustrative embodiment of amulti-terminal output with a common mode connection is depicted andgenerally designated 100. The multi-terminal output with a common modeconnection 100 is a circuit that includes an output element 102 having afirst terminal 104 and a second terminal 106. A transistor 108 iscoupled to the first terminal 104 via a first resistive element 110. Asecond resistive element 112 is coupled to the transistor 108 and to thesecond terminal 106. A third resistive element 114 is coupled to thefirst terminal 104 and is coupled to a fourth resistive element 116 viaa node 120. The fourth resistive element 116 is coupled to the secondterminal 106. The node 120 represents a common mode connection 122 ofthe first terminal 104 and the second terminal 106. The node 120 iscoupled to a bulk connection of the transistor 108. Coupling of the bulkconnection of the transistor 108 to the node 120 allows the transistor108 to accommodate a large gate bias at the gate of the transistor 108.A bulk bias (vbulk) at node 120 may be a common mode voltage of thefirst terminal 104 and the second terminal 106.

In a particular embodiment, the output element 102 may be coupled to adriver, may be part of a driver, or may be an output driver inside atransmitter, such as a high-definition multimedia interface (HDMI)compliant transmitter. For example, the output element 102 may apply adifferential signal at the first terminal 104 and the second terminal106. The first terminal 104 may be coupled to a drain terminal of atransistor that is inside the output element 102 and the second terminal106 may be coupled to a drain terminal of another transistor that isinside the output element 102, as described with respect to FIG. 2. Theoutput element 102 may be coupled to a receiver side (not shown) viatransmission lines as described in further detail with respect to FIG.2. The output element 102 may be configured to operate at a supplyvoltage that is lower than a supply voltage used at the receiver side.In a particular non-limiting example, the output element 102 may operateat a supply voltage of approximately 1.8 volts while coupled to areceiver side that operates at 3.3 volts.

In a particular embodiment, the first resistive element 110 and thesecond resistive element 112 may be resistors. The first resistiveelement 110, the transistor 108, and the second resistive element 112may be components in a resistor network, alternatively referred to as aresistive network herein. The resistor network is controlled to adjustthe output impedance of the multi-terminal output with a common modeconnection 100.

In a particular embodiment, the third resistive element 114 mayrepresent one or more resistors, and the fourth resistive element 116may represent one or more resistors. The node 120 between thirdresistive element 114 and the fourth resistive element 116 representsthe common mode connection 122 of the first terminal 104 and the secondterminal 106.

As illustrated, the transistor 108 is coupled to the first resistiveelement 110 and the second resistive element 112. The transistor 108 isconfigured to receive an impedance control signal imp<x> at a gate ofthe transistor 108. The impedance control signal imp<x> may be levelshifted to a power domain that is based on a supply voltage used by thereceiver side. In a particular embodiment, the transistor 108 may be atransistor inside a transmitter, such as a high-definition multimediainterface (HDMI) compliant transmitter.

The transistor 108 may be fabricated to operate at a lower supplyvoltage (e.g. 1.8 volts) without requiring the bulk connection of thetransistor 108 to be coupled to a particular voltage supply. In aparticular embodiment, the transistor 108 may be a p-channel metal oxidesemiconductor (PMOS) transistor. For example, the transistor 108 mayhave a requirement that a voltage difference between any of its fourterminals (i.e., drain, source, gate, and bulk) not exceed a particularvoltage in order for the transistor to operate with a high reliability.By coupling the bulk connection of the transistor 108 to the common modeconnection 122, the transistor 108 may operate at a higher voltage thanthe lower supply voltage associated with the output element 102 whileclosely maintaining the reliability of the transistor. Since the bulkconnection is coupled to the common mode connection 122, the transistor108 may operate at a higher supply voltage that may be used by thereceiver side and still closely maintain its reliability.

During operation, the output element 102 provides output signals to theterminals 104 and 106. The resistive elements 114 and 116 provide acommon mode voltage at the node 120 that is provided to the bulkconnection of the transistor 108. The transistor 108 may be turned ondepending on the impedance control signal imp<x> that is provided to thegate of the transistor 108. If the transistor 108 is turned on, theresistive elements 110 and 112 contribute to an output impedance of themulti-terminal output with a common mode connection 100. Turning off thetransistor 108 may substantially reduce or eliminate the contribution ofthe resistive elements 110 and 112 to the output impedance.

The output impedance may be adjusted to match or substantially match theoutput impedance of the multi-terminal output with a common modeconnection 100 with an impedance of transmission lines coupled to theoutput element 102. When the output element 102 is coupled to a receiverside that uses a receiver supply voltage that is higher than a supplyvoltage that is used at the output element 102, the reliability of thetransistor 108 may be closely maintained by providing the bulk bias(vbulk) at node 120 to the bulk connection of the transistor 108.

To illustrate, the bulk bias (vbulk) at the node 120 may represent avoltage that is close in level to a receiver supply voltage used at areceiving device (e.g., 3.3 volts). By applying the bulk bias (vbulk),which may be close to the receiver supply voltage (e.g., 3.3 volts), tothe bulk connection of the transistor 108, an operating point of thetransistor 108 may fall within design criteria to provide the highreliability of the transistor 108 (as compared to operating at the highvoltage supply without the bulk connection coupled to the common modeconnection 122).

By providing the impedance control signal (imp<x>) to the gate of thetransistor 108, an output impedance may be adjusted to substantiallymatch an impedance of transmission lines that are coupled to the firstoutput terminal 104 and the second output terminal 106 while reducingreliability risks associated with receivers that operate at a highersupply voltage. Further, by generating the common mode voltage (vbulk)at the common mode connection 122 of the output element 102 between thefirst terminal 104 and the second terminal 106 and providing the commonmode voltage (vbulk) to the bulk connection of the transistor 108, atransmitting device that incorporates the multi-terminal output with acommon mode connection 100 may be operated at a lower power supply whileusing an open drain output that is coupled to a receiving device thatoperates at a higher supply voltage, such as a receiving device thatoperates according to an HDMI standard. Lower voltage supplies andsmaller devices may be used in transmitter devices without substantiallyreducing a reliability of transistors in the resistor network, such asthe transistor 108. As a result, lower power operation and increaseddevice reliability may be obtained.

Referring to FIG. 2, an illustrative embodiment of a system thatincludes a driver 202 is depicted and generally designated 200. Thedriver 202 is an output driver and is an illustrative implementation ofthe multi-terminal output with a common mode connection 100 of FIG. 1.The system 200 also includes transmission lines 250, 252 and a receiverside 204. The driver 202 is coupled to the receiver side 204 via thetransmission lines 250, 252.

The driver 202 is a circuit that includes a resistor network 240 that iscoupled between the first terminal 104 and the second terminal 106. Thefirst terminal 104 is coupled to a drain of a first transistor 236. Adrain of a second transistor 238 is coupled to the second terminal 106.A source of the first transistor 236 is coupled to a drain of a thirdtransistor 232. A source of the third transistor 232 is coupled to acurrent source 242. A source of the second transistor 238 is coupled toa drain of a fourth transistor 234. A source of the fourth transistor234 is coupled to the current source 242.

A gate of the first transistor 236 and a gate of the second transistor238 are coupled to receive a gate bias signal (vbias). An output buffer230 generates an inverted output signal that is provided to a gate ofthe fourth transistor 234 and a non-inverted output signal that isprovided to a gate of the third transistor 232. A driver supply voltage(not shown) may be provided to the output buffer 230.

The first terminal 104 is coupled to a first transmission line 250, andthe second terminal 106 is coupled to a second transmission line 252.The first transmission line 250 is coupled to a receiver side 204 thatincludes a first pull up resistor 260 and a receiver 270. The secondtransmission line 252 is coupled to a second pull up resistor 262 and tothe receiver 270. An output impedance of the driver 202 may be adjustedby controlling one or more input signals (imp<n:0>) provided to theresistor network 240, where n is a positive integer. A value of n maycorrespond to an amount of precision that can be applied when adjustingthe output impedance of the driver 202.

In a particular embodiment, the first transistor 236 and the secondtransistor 238 provide an open drain output of the driver 202 to thetransmission lines 250 and 252. The first transistor 236 and the secondtransistor 238 are respectively responsive to the third transistor 232and to the fourth transistor 234. The output buffer 230 is configured togenerate a differential signal that includes the non-inverting outputsignal and the inverting output signal. The third transistor 232 and thefourth transistor 234 are respectively controlled by the non-invertingoutput signal and the inverting output signal.

In a particular embodiment, the resistor network 240 includes a firstresistive element 210 and a second resistive element 212. The firstresistive element 210 may be coupled to the first terminal 104, and thesecond resistive element 212 may be coupled to the second terminal 106.In addition, the first resistive element 210 and the second resistiveelement 212 may each be coupled to a transistor 208. The transistor 208may have a gate that is responsive to at least one of the impedancecontrol signals (imp<n:0>) and may have a bulk connection that iscoupled to a common mode connection, such as the common mode connection122 of FIG. 1. The bulk bias (vbulk) may be provided to the bulkconnection of the transistor 208. Further detail of a particularembodiment of the resistor network 240 is provided with reference toFIG. 3.

The first pull up resistor 260 is configured to provide a pull upvoltage (VDDrx) to the first transmission line 250, and the second pullup resistor 262 is configured to provide the pull up voltage (VDDrx) tothe second transmission line 252. As a result of the pull up operationby the pull up resistors 260 and 262, a voltage at the first terminal104 and a voltage at the second terminal 106 may be pulled up close tothe pull up voltage (VDDrx). The receiver 270 may receive thedifferential signal from the driver 202 via a first input 264 that iscoupled to the first transmission line 250 and via a second input 266that is coupled to the second transmission line 252.

During operation, a supply voltage (not shown) is provided to the outputbuffer 230. Transitions in buffer input signals (inp) and (inn) maycause the non-inverting output signal and the inverting output signalgenerated by the output buffer 230 to toggle. The non-inverting outputsignal and the inverting output signal may turn on the third transistor232 and the fourth transistor 234 respectively. The gate bias signal(vbias) may turn on the first transistor 236 and the second transistor238. The voltage at the first terminal 104 and the voltage at the secondterminal 106 may be pulled up close to the pull up voltage (VDDrx) bythe pull up resistors 260 and 262 that are respectively coupled to thetransmission lines 250 and 252. Since the first transistor 236 and thesecond transistor 238 are coupled to the first terminal 104 and thesecond terminal 106, transmission power loss may occur withoutadjustment of the output impedance of the driver 202. The outputimpedance of the driver 202 may be adjusted by controlling the impedancecontrol signals (imp<n:0>). Because the voltage at the first terminal104 and the voltage at the second terminal 106 may be pulled up close tothe pull up voltage (VDDrx), the impedance control signals (imp<n:0>)may be level shifted to a power domain that is based on the pull upvoltage (VDDrx).

By controlling the impedance control signals (imp<n:0>), the outputimpedance of the driver 202 may be adjusted to match or substantiallymatch an impedance of the transmission lines 250 and 252. For example,by turning on the transistor 208, the first resistive element 210 andthe second resistive element 212 may contribute to the output impedanceof the driver 202. Similarly, by turning off the transistor 208, thecontribution of the first resistive element 210 and the second resistiveelement 212 to the output impedance of the driver 202 may besignificantly reduced or eliminated. Further, by providing the bulk bias(vbulk) to the bulk connection of the transistor 208 in the resistornetwork 240, the voltage at the first terminal 104 and the voltage atthe second terminal 106 may be pulled up to a voltage that may otherwisereduce a reliability of the transistor 208. Further, by providing thebulk bias (vbulk) to the bulk connection of the transistor 208, atransmitting device that incorporates the driver 202 may be operated ata lower power supply while using an open drain output that is coupled toa receiving device that operates at a higher supply voltage, such as areceiving device that operates according to an HDMI standard. Lowervoltage supplies and smaller devices may be used in transmitter deviceswithout reducing or substantially reducing a reliability of transistors,such as the transistor 208, that are coupled to the resistive elements210 and 212 in the resistor network 240. As a result, lower poweroperation and increased device reliability may be obtained.

Referring to FIG. 3, a particular embodiment of a resistor network isdepicted and generally designated 300. In an illustrative embodiment,the resistor network 300 may be used for the resistor network 240 ofFIG. 2. The resistor network 300 includes the first terminal 104 and thesecond terminal 106. A first resistor 310 is coupled to the firstterminal 104 and to a first transistor 308. A second resistor 312 iscoupled between the second terminal 106 and the first transistor 308. Athird resistor 320 is coupled between the first terminal 104 and asecond transistor 318. A fourth resistor 322 is coupled between thesecond terminal 106 and the second transistor 318. A fifth resistor 330is coupled between the first terminal 104 and a third transistor 328. Asixth resistor 332 is coupled between the second terminal 106 and thethird transistor 328. The transistors 308, 318, and 328 areindependently biasable and may be individually activated or deactivatedto obtain an impedance between the first terminal 104 and the secondterminal 106. The impedance between the first terminal 104 and thesecond terminal 106 may contribute to the output impedance of an output,such as an output impedance of the driver 202 of FIG. 2. Because of thecontribution of the impedance between the first terminal 104 and thesecond terminal 106, the output impedance of the driver 202 may beadjusted to match or substantially match the impedance of thetransmission lines 250 and 252 depicted in FIG. 2.

Impedance control signals, such as the imp<n:0> of FIG. 2, may bereceived at the resistor network 300. A first component (imp<0>) of theimpedance control signals may be provided to a gate of the thirdtransistor 328, a second component (imp<1>) of the impedance controlsignals may be provided to a gate of the second transistor 318, and ann^(th) component (imp<n>) of the impedance control signals may beprovided to a gate of the first transistor 308. The impedance controlsignals (imp<n:0>) may be level shifted to a power domain that is basedon a receiver side voltage, such as the pull up voltage (VDDrx) of FIG.2. Each of the impedance control signals (imp<n:0>) may be a digitalsignal that selectively activates or deactivates a respective transistor308, 318, 328. In a particular embodiment, the first component (imp<0>)corresponding to a first impedance control signal, the second component(imp<1>) corresponding to a second impedance control signal, and thethird component (imp<n>) corresponding to a third impedance controlsignal. The impedance control signals may have a rail voltage that issubstantially the same as a common mode voltage of a common modeconnection.

Each of the transistors 308, 318, and 328 may be designed to operatewith the bulk connection of the particular transistor coupled to thecommon mode connection or with the bulk connection of the particulartransistor not coupled to the common mode connection. Each transistor308, 318, 328 may have a high reliability if a voltage between a drainof the transistor 308, 318, 328 and a bulk connection of the transistor308, 318, 328 and a voltage between the source of the transistor 308,318, 328 and the bulk connection of the transistor 308, 318, 328 arebelow a threshold voltage. However, a reliability of the transistor 308,318, 328 may be reduced if the voltage difference between the drain ofthe transistor 308, 318, 328 and the bulk connection of the transistor308, 318, 328 and the voltage between the source of the transistor 308,318, 328 and the bulk connection of the transistor 308, 318, 328 exceedsthe threshold voltage. When the drain and the source of a particulartransistor 308, 318, or 328 are coupled to a low voltage supply,operating the particular transistor 308, 318, or 328 with the bulkconnection of the particular transistor 308, 318, or 328 not coupled tothe common mode connection may not reduce a reliability of theparticular transistor 308, 318, or 328. When the drain and the source ofa transistor 308, 318, or 328 are coupled to a high voltage supply,providing the bulk bias (vbulk) to the bulk connection of the transistor308, 318, or 328 may maintain the voltage between the drain/source ofthe transistor 308, 318, 328 and the bulk connection of the transistor308, 318, 328 below the threshold voltage.

To illustrate, each transistor 308, 318, 328 may be designed to operatewith a high reliability at a 1.8 volt supply without coupling the bulkconnection of the transistor 308, 318, 328 to a common mode connection.However, when the first and second terminals 104, 106 are coupled to thepull up resistors 260 and 262 of FIG. 2 via the transmission lines 250and 252 of FIG. 2, the voltage at the first and second terminals 104,106 may exceed 1.8 volts. For example, the voltage at the first terminal104 and the voltage at the second terminal 106 may be close to 3.3 voltsas a result of the pull up resistors 260 and 262 and the supply voltage(VDDrx) of FIG. 2. The bulk connections of each of the transistors 308,318, and 328 may be coupled to common node connections, such as thecommon node connection at the node 120 illustrated in FIG. 1. Bycoupling the bulk connection of each of the transistors 308, 318, 328 tothe common mode connection, the transistors 308, 318, 328 may operatewhile maintaining a high reliability. Operating the transistors 308,318, 328 without coupling the bulk connection of the transistors 308,318, and 328 to a common mode connection may reduce a reliability of thetransistors 308, 318, and 328.

During operation, the voltage at the first terminal 104 and the voltageat the second terminal 106 may be pulled up close to the receiver sidevoltage, such as the pull up voltage (VDDrx) of FIG. 2. The bulk bias(vbulk) may be provided to the bulk connection of the transistors 308,318, and 328. The components (imp<0>, imp<1>, and imp<n>) of theimpedance control signals (imp<n:0>) may turn on or turn offcorresponding transistors 308, 318, and 328. The resistor pairs 310/312,320/322, and 330/332 that are coupled to the transistors 308, 318, and328 that are turned on may contribute to the impedance between the firstterminal 104 and the second terminal 106. In turn, the impedance betweenthe first terminal 104 and the second terminal 106 may contribute to theoutput impedance of an output, such as the driver 202 of FIG. 2. Becauseof a contribution of the impedance between the first terminal 104 andthe second terminal 106, the output impedance of the driver 202 maymatch or substantially match the impedance of the transmission lines in250 and 252 depicted in FIG. 2.

By controlling the impedance control signals (imp<n:0>), the impedancebetween the first terminal 104 and the second terminal 106 may beadjusted to contribute to an output impedance of an output, such as thedriver 202 of FIG. 2, so that the output impedance of the output matchesor substantially matches an impedance of the transmission lines 250 and252. Further, by providing the bulk bias (vbulk) to the bulk connectionof the transistors 308, 318, and 328, the voltage at the first terminal104 and the voltage at the second terminal 106 may be pulled up to avoltage that may otherwise reduce a reliability of the transistors 308,318, and 328. Thus, a transmitting device that incorporates a driver,such as the driver 202, may be provided a lower power supply at thetransmitting device side while coupled to a receiving device thatoperates at a higher supply voltage, such as a receiving device thatoperates according to an HDMI standard.

Although FIG. 3 illustrates three transistors 308, 318, and 328 and thecorresponding resistor pairs 310/312, 320/322, and 330/332, the numberof transistors and corresponding resistor pairs may be fewer than threeor more than three in alternative embodiments.

Referring to FIG. 4, a particular embodiment of a calibration system isdepicted and generally designated 400. The system 400 is configured toprovide impedance control signals (imp<n:0>) that may be provided to theresistor network 240 of FIG. 2 and 300 of FIG. 3. The system 400includes a calibration component 402 coupled to a level shiftingcomponent 422. The calibration component 402 provides control signals(ctrl<n:0>) 424 to the level shifting component 422. The calibrationcomponent 402 is in a first power domain that is based on a supplyvoltage (VDDX). For example, the supply voltage (VDDX) may be 1.8 volts.The level shifting component 422 is in a second power domain that isbased on the bulk bias (vbulk) 428 corresponding to a common modevoltage at a common mode connection, such as the common mode connection122 of FIG. 1. For example, the bulk bias (vbulk), which is a commonmode voltage, may be close to 3.3 volts.

The calibration component 402 includes an operational amplifier 412coupled to an input of a counter 414. The counter 414 generates thecontrol signals (ctrl<n:0>) 424 that are provided to a first set oftransistors 434. The first set of transistors 434 is in the first powerdomain and includes a first transistor 420, a second transistor 418, anda third transistor 416. The control signals (ctrl<n:0>) 424 are providedto gates of the first transistor 420, the second transistor 418, and thethird transistor 416, and to the level shifting component 422. Thecontrol signals (ctrl<n:0>) 424 may have a rail voltage level associatedwith the first power domain. Each transistor 416, 418, 420 is coupled toa path between the supply voltage (VDDX) and ground. The outputs of thetransistors 416, 418, 420 are coupled to a resistor network 408 andprovide impedance signals (imp_(—)1<n:0>) to the resistor network 408.The supply voltage (VDDX) is provided to a first terminal (term1) of theresistor network 408. A second terminal (term2) of the resistor network408 is coupled to a first input of the operational amplifier 412. Asecond input of the operational amplifier 412 is coupled to acalibration resistive element 410. The supply voltage (VDDX) is alsoprovided to the calibration resistive element 410.

The calibration resistive element 410 may be a configurable resistorthat may have a configurable resistance. Alternatively, the calibrationresistive element 410 may be a resistor that can be easily swapped withanother resistor of the same or different resistance. The calibrationresistive element 410 may be selected to obtain a desired impedancebetween the first and second terminals 104, 106 of FIGS. 2 and 3 bycontrolling the impedance control signals (imp<n:0>) 426 that aregenerated based on the control signals (ctrl<n:0>) 424 and provided tothe resistor network 240 of FIGS. 2 and 300 of FIG. 3. In a particularembodiment, the calibration resistive element 410 may be a resistor thatis external to the calibration system 400.

The level shifting component 422 includes a second set of transistors404, a third set of transistors 406, and a set of resistive elements430. The second set of transistors 404 is in the second power domain andincludes a fourth transistor 436, a fifth transistor 438, and a sixthtransistor 440, and the third set of transistors 406 includes a seventhtransistor 446, an eighth transistor 448, and a ninth transistor 450.The second set of transistors 404 is responsive to the first set oftransistors 434 and controls a resistor network (e.g., the resistornetwork 240 of FIG. 2 or 300 of FIG. 3). Each transistor 436, 438, 440in the second set of transistors 404 is coupled to a component of thecontrol signals (ctrl<n:0>) 424. A gate of the fourth transistor 436 iscoupled to a first component (ctrl<0>), a gate of the fifth transistor438 is coupled to a second component (ctrl<1>), and a gate of the sixthtransistor 440 is coupled to an n^(th) component (ctrl<n>). Eachtransistor 436, 438, 440 in the second set of transistors 404 is coupledto a corresponding transistor 446, 448, or 450 in the third set oftransistors 406. For example, the fourth transistor 436 is coupled tothe seventh transistor 446, the fifth transistor 438 is coupled to theeighth transistor 448, and the sixth transistor 440 is coupled to theninth transistor 450. The bulk bias (vbulk) is provided to the third setof transistors 406 via the set of resistive elements 430 and the secondset of transistors 406.

The supply voltage (VDDX) is provided to a gate of each transistor 446,448, 450 in the third set of transistors 406. The outputs of transistors446, 448, 450 combine to provide the impedance control signals(imp<n:0>) 426 that are provided to the resistor network 240 of FIG. 2and 300 of FIG. 3. The impedance control signals (imp<n:0>) 426 have asecond rail voltage level associated with the second power domain. Thebulk bias (vbulk) is provided to the third set of transistors 406 viathe set of resistive elements 430. Each resistive element in the set ofresistive elements 430 has a first terminal that is biased at the bulkbias (vbulk). Each transistor 446, 448, or 450 in the third set oftransistors 406 is coupled to a second terminal of a correspondingresistive element in the set of resistive elements 430.

During operation, the operational amplifier 412 may generate a signalthat is provided to the counter 414. The operational amplifier 412generates the signal based on the first and second inputs of theoperational amplifier 412, which are respectively coupled to theresistor network 408 and the calibration resistive element 410. Thecounter 414 may change the control signals (ctrl<n:0>) 424 based on afirst value of the signal from the operational amplifier 412. Thecounter 414 may stop changing the control signals (ctrl<n:0>) 424 basedon a second value of the signal from the operational amplifier 412. Forexample, the counter may change the control signals (ctrl<n:0>) 424 ifthe signal from the operational amplifier 412 is high and may stopchanging the control signals (ctrl<n:0>) 424 if the signal from theoperational amplifier 412 is low. The control signals (ctrl<n:0>) 424may have a rail voltage level (e.g., 1.8 volts) that is close to thesupply voltage (VDDX).

The transistors 416, 418, 420 may be turned on or turned off dependingon the control signals (ctrl<n:0>) 424. The impedance signals(<imp_(—)1<n:0>) that are coupled to the resistor network 408 aregenerated according to which ones of the transistors 416, 418, 420 inthe first set of transistors 434 are turned on or turned off by thecontrol signals (ctrl<n:0>) 424. The control signals (ctrl<n:0>) 424 arealso provided to the second set of transistors 404 that are coupled tothe third set of transistors 406. The third set of transistors 406 maybe turned on by the supply voltage (VDDX). Each transistor 436, 438, 440in the second set of transistors 404 may be turned on or turned offdepending on the control signals (ctrl<n:0>) 424. By turning on or offthe transistors 436, 438, and 440 in the second set of transistors 404,the control signals (ctrl<n:0>) 424 control the impedance controlsignals (imp<n:0>) 426 provided to the resistor network 240 of FIG. 2and 300 of FIG. 3. Since the bulk bias (vbulk) is provided to the thirdset of transistors 406, the impedance control signals (imp<n:0>) 426 mayhave a rail voltage level (e.g., 3.3 volts) that is close to the bulkbias (vbulk).

The impedance control signals (imp<n:0>) 426 are provided to a resistornetwork, (e.g., the resistor network 240 of FIG. 2 or 300 of FIG. 3).Transistors (e.g., the transistors 308, 318, 328 of FIG. 3) in theresistor network are coupled to the first and second terminals 104 and106 of FIGS. 1-3. Since a voltage at the first and second terminals 104and 106 may be pulled up close to a receiver side voltage (e.g., 3.3volts), the impedance control signals (imp<n:0>) that have a railvoltage level that is close to the bulk bias (vbulk) (e.g., 3.3 volts)enable a normal operation of the transistors. In turn, the normaloperation of the transistors enables adjustment of the impedance betweenthe first terminal 104 and the second terminal 106 of FIGS. 1-3.

Although FIG. 4 illustrates an input to the counter 414 being providedby the operational amplifier 412, in other embodiments the input to thecounter 414 may be provided by a comparator. Further, while threetransistors 416, 418, and 420 are shown in the calibration component402, the number of transistors may be fewer than three or more thanthree in alternative embodiments. For example, one or two transistorsmay be used. Similarly, the number of transistors in the second andthird sets of transistors 404 and 406 may include more than threetransistors or fewer than three transistors.

Referring to FIG. 5, a particular embodiment of a system that includesmultiple drivers is depicted and generally designated 500. The system500 includes a first driver 502, a second driver 504, a third driver506, and fourth driver 508. Each of the drivers 502, 504, 506, and 508is coupled to a receiver side circuit 570 via transmission linesillustrated as a first transmission line pair 520, a second transmissionline pair 522, a third transmission line pair 524, and a fourthtransmission line pair 526. The impedance calibration engine 510 isconfigured to provide impedance control signals (imp<n:0>) to thedrivers 502, 504, 506, and 508. The impedance calibration engine 510 mayadjust the impedance control signals (imp<n:0>) to adjust impedance ofthe drivers 502, 504, 506, and 508. For example, the impedancecalibration engine 510 may correspond to the system 400 illustrated inFIG. 4.

In a particular embodiment, each of the drivers 502, 504, 506, 508corresponds to the driver 202 of FIG. 2. In a particular embodiment, thefirst driver 502 may be a clock driver. The first driver 502 includes anoutput buffer having an inverting output and a non-inverting output thatare used to drive transistors that are coupled to open draintransistors. The open drain transistors are coupled to first and secondterminals. The first driver 502 also includes a resistor network 540,which may correspond to the resistor network 300 of FIG. 3. Asillustrated, the resistor network 540 may be coupled to a first outputterminal and a second output terminal of the first driver 502. Theresistor network 540 may be responsive to the impedance control signals(imp<n:0>) that are used to adjust an impedance of the first driver 502to match or substantially match an impedance of the transmission linepair 520. The bulk connections of transistors in the resistor network540 are coupled to a common mode connection of the output terminals ofthe first driver 502. Coupling the bulk connection of the transistors inthe resistor network 540 to a common mode connection preserves areliability of the transistors in the event pull up voltage (VDDrx) usedat the receiver side 570 would pose a risk to the reliability of thetransistors, such as described with respect to FIGS. 2 and 3. Each ofthe other drivers 504, 506, and 508 operates in a similar manner asdescribed above with respect to driver 502 and the driver 202 of FIG. 2.In a particular embodiment, each of the drivers 504, 506, and 508 may bea data driver. Each driver 504, 506, 508 includes a resistor network 540that is coupled to a first output terminal and a second output terminalof each driver 504, 506, 508.

As illustrated, the system 500 of FIG. 5 may be incorporated in an HDMItransmitter, where the first driver 502 corresponds to a clock driver,the second driver 504 corresponds to a red driver, the third driver 506corresponds to a green driver, and the fourth driver 508 corresponds toa blue driver.

During operation, the impedance calibration engine 510 provides theimpedance control signals (imp<n:0>) to the drivers 502, 504, 506, and508. The impedance control signals (imp<n:0>) may adjust the outputimpedances of each of the drivers 502, 504, 506, and 508. The bulk bias(vbulk) is provided to the resistor network 540 inside the drivers 504,506, and 508. A common mode voltage at the common mode connection of theoutputs of the first driver 502 is provided to the resistor network 540inside the first driver 502. Each driver 502, 504, 506, and 508generates output signals for transmission to the receiver side 570 viacorresponding transmission lines 520, 522, 524, and 526.

Output impedances of the drivers 502, 504, 506, and 508 may be adjustedto match or substantially match the impedances of correspondingtransmission line pairs 520, 522, 524, and 526. By adjusting an outputimpedance of the first driver 502 to match or substantially match animpedance of the transmission line pair 520, reflection loss due toimpedance mismatch between the first driver 502 and the firsttransmission line pair 520 may be reduced. Similarly, reflection lossesdue to impedance mismatch between the other drivers 504, 506, and 508and their corresponding transmission line pairs 522, 524, and 526 mayalso be reduced. Further, by coupling the bulk connections oftransistors inside each resistor network 540, the reliability of thetransistors in each resistor network 540 may be substantiallymaintained.

Referring to FIG. 6, a particular illustrative embodiment of a method ofoperating a multi-terminal output with a common mode connection isillustrated. The method 600 includes generating a first set of controlsignals, at 602. For example, the control signals (ctrl<n:0>) 424 may begenerated by the calibration component 402 of FIG. 4. Each of the firstset of control signals has a first rail voltage level associated with afirst power domain. For example, the control signals (ctrl<n:0>) 424 mayhave a rail voltage level that is associated with the first power domainof FIG. 4.

The method 600 further includes generating a second set of controlsignals from the first set of control signals, at 604. For example, theimpedance control signals (imp<n:0>) 426 of FIG. 4 may be generated bythe level shift component 422 of FIG. 4. Each of the second set ofcontrol signals has a second rail voltage level that is associated witha second power domain. The second power domain is associated with acommon mode voltage of output terminals of an output driver. Forexample, the impedance control signals (imp<n:0>) 426 may have a railvoltage level that is associated with the second power domain of FIG. 4.The second power domain may be associated with the bulk bias (vbulk),which may be provided by the common mode connection of the first andsecond terminals 104 and 106 of the multi-terminal output with a commonmode connection of FIG. 1. In a particular embodiment, the second railvoltage level that is associated with the second power domain is higherthan the first rail voltage level that is associated with the firstpower domain.

The method 600 of FIG. 6 may be implemented by an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA)device, a processing unit such as a central processing unit (CPU), adigital signal processor (DSP), a controller, another hardware device,firmware device, or any combination thereof. As an example, the methodof FIG. 4 can be performed by a processor that executes instructions, asdescribed with respect to FIG. 7.

Referring to FIG. 7, a block diagram of a particular illustrativeembodiment of a wireless communication device is depicted and generallydesignated 700. The device 700 includes a processor unit 710, such as adigital signal processor (DSP), coupled to a memory 732 and a wirelesscontroller 740. The device 700 may include one or more drivers (e.g., adriver with adjustable output impedance 764) coupled to the processorunit 710. In an illustrative embodiment, the driver with adjustableoutput impedance 764 may correspond to the multi-terminal output with acommon mode connection 100 of FIG. 1, the driver 202 of FIG. 2, thedriver 502 of FIG. 5, the driver 504 of FIG. 5, the driver 506 of FIG.5, or the driver 508 of FIG. 5, or may operate according to the methodof FIG. 6, or any combination thereof. In a particular embodiment, thedriver with adjustable output impedance 764 may be coupled totransmission lines 750 and 752. Although the driver with adjustableoutput impedance 764 is illustrated as coupled to the processor unit710, in other embodiments, the driver with adjustable output impedance764 may be integrated within the processor unit 710.

The memory 732 may be a non-transient computer readable medium storingcomputer-executable instructions 756 that are executable by theprocessor unit 710 to cause the processor unit 710 to process datareceived via a wireless controller 740. For example, the received datamay be based on voice or video signals received via a wireless antenna742. The computer-executable instructions 756 may include instructionsthat are executable by the processor unit 710 to cause the processorunit 710 to process received data and to generate output data that isformatted for audio output. The computer-executable instructions 756 mayalso include instructions that are executable by the processor unit 710to cause the processor unit 710 to process received data and to generateoutput data that is formatted for display.

In a particular illustrative embodiment, the computer-executableinstructions 756 may include instructions that are executable by theprocessor unit 710 to cause the processor unit 710 to generate a firstset of control signals, where each of the first set of control signalshas a first rail voltage level associated with a first power domain. Thefirst set of control signals may be generated based on a resistor thathas a configurable resistance. The resistor may be inside the driverwith adjustable output impedance 764, or inside a transmitter, such as ahigh-definition multimedia interface (HDMI) compliant transmitter thatis coupled to the processing unit 710. The computer-executableinstructions 756 may also include instructions that are executable bythe processor unit 710 to cause the processor unit 710 to generate asecond set of control signals from the first set of control signals,where each of the second set of control signals has a second railvoltage level that is associated with a second power domain and wherethe second power domain is associated with a common mode voltage ofoutputs of the driver with adjustable output impedance 764. The secondset of control signals may be used to adjust an output impedance of thedriver with adjustable output impedance 764, such as described withrespect to FIG. 4. In another embodiment, logic to generate the controlsignals is within the driver 764 instead of being implemented by some ofthe instructions 756. The logic within the driver 764 may includecircuit elements as illustrated by the circuit 400 in FIG. 4.

FIG. 7 also shows a display controller 726 that is coupled to thedigital signal processor unit 710 and to a display 728. A coder/decoder(CODEC) 734 can also be coupled to the processor unit 710. A speaker 736and a microphone 738 can be coupled to the CODEC 734.

FIG. 7 also indicates that the wireless controller 740 can be coupled tothe wireless antenna 742. In a particular embodiment, the processor unit710, the display controller 726, the memory 732, the CODEC 734, thedriver with adjustable output impedance 764, and the wireless controller740 are included in a system-in-package or system-on-chip device 722. Ina particular embodiment, an input device 730 and a power supply 744 arecoupled to the system-on-chip device 722. Moreover, in a particularembodiment, as illustrated in FIG. 7, the display 728, the input device730, the speaker 736, the microphone 738, the wireless antenna 742, andthe power supply 744 are external to the system-on-chip device 722.However, each of the display 728, the input device 730, the speaker 736,the microphone 738, the wireless antenna 742, and the power supply 744can be coupled to a component of the system-on-chip device 722, such asan interface or a controller.

While FIG. 7 illustrates a particular embodiment of a wireless device700, one or more drivers (e.g., the driver with adjustable outputimpedance 764) may be integrated in other electronic devices including aset top box, a music player, a video player, an entertainment unit, anavigation device, a communications device, a personal digital assistant(PDA), a fixed location data unit, and a computer integrated.

In conjunction with the described embodiments, a system is disclosedthat may include means for generating a common mode voltage at a commonmode connection, where the common mode connection is between a firstterminal and a second terminal, such as the resistive elements 114, 116of FIG. 1, the resistive elements 530, 532, 536, 538 of FIG. 5, one ormore other devices or circuits configured to generate a common modevoltage at a common mode connection, or any combination thereof. Thesystem may also includes means for adjusting an output impedance basedon a first input and the common mode voltage, such as the transistor 108of FIG. 1, the resistor network 240 of FIG. 2, the resistor network 300of FIG. 3, one or more other devices or circuits configured to adjust anoutput impedance based on a first input and the common mode voltage, orany combination thereof.

The foregoing disclosed devices and functionalities may be designed andconfigured into computer files (e.g. RTL, GDSII, GERBER, etc.) stored oncomputer readable media. Some or all such files may be provided tofabrication handlers who fabricate devices based on such files.Resulting products include semiconductor wafers that are then cut intosemiconductor die and packaged into a semiconductor chip. The chips arethen employed in devices described above. FIG. 8 depicts a particularillustrative embodiment of an electronic device manufacturing process800.

Physical device information 802 is received at the manufacturing process800, such as at a research computer 806. The physical device information802 may include design information representing at least one physicalproperty of a semiconductor device, such as the multi-terminal outputwith a common mode connection of FIG. 1, the driver 202 of FIG. 2, theresistor network 300 of FIG. 3, the calibration block 400 of FIG. 4, thedrivers 502, 504, 506, and 508 of FIG. 5, or any combination thereof.For example, the physical device information 802 may include physicalparameters, material characteristics, and structure information that isentered via a user interface 804 coupled to the research computer 806.The research computer 806 includes a processor 808, such as one or moreprocessing cores, coupled to a computer readable medium such as a memory810. The memory 810 may store computer readable instructions that areexecutable to cause the processor 808 to transform the physical deviceinformation 802 to comply with a file format and to generate a libraryfile 812.

In a particular embodiment, the library file 812 includes at least onedata file including the transformed design information. For example, thelibrary file 812 may include a library of semiconductor devicesincluding a device that includes the multi-terminal output with a commonmode connection of FIG. 1, the driver 202 of FIG. 2, the resistornetwork 300 of FIG. 3, the calibration block 400 of FIG. 4, the drivers502, 504, 506, and 508 of FIG. 5, or any combination thereof, that isprovided for use with an electronic design automation (EDA) tool 820.

The library file 812 may be used in conjunction with the EDA tool 820 ata design computer 814 including a processor 816, such as one or moreprocessing cores, coupled to a memory 818. The EDA tool 820 may bestored as processor executable instructions at the memory 818 to enablea user of the design computer 814 to design a circuit including themulti-terminal output with a common mode connection of FIG. 1, thedriver 202 of FIG. 2, the resistor network 300 of FIG. 3, thecalibration block 400 of FIG. 4, the drivers 502, 504, 506, and 508 ofFIG. 5, or any combination thereof, of the library file 812. Forexample, a user of the design computer 814 may enter circuit designinformation 822 via a user interface 824 coupled to the design computer814. The circuit design information 822 may include design informationrepresenting at least one physical property of a semiconductor device,such as the multi-terminal output with a common mode connection of FIG.1, the driver 202 of FIG. 2, the resistor network 300 of FIG. 3, thecalibration block 400 of FIG. 4, the drivers 502, 504, 506, and 508 ofFIG. 5, or any combination thereof. To illustrate, the circuit designproperty may include identification of particular circuits andrelationships to other elements in a circuit design, positioninginformation, feature size information, interconnection information, orother information representing a physical property of a semiconductordevice.

The design computer 814 may be configured to transform the designinformation, including the circuit design information 822, to complywith a file format. To illustrate, the file formation may include adatabase binary file format representing planar geometric shapes, textlabels, and other information about a circuit layout in a hierarchicalformat, such as a Graphic Data System (GDSII) file format. The designcomputer 814 may be configured to generate a data file including thetransformed design information, such as a GDSII file 826 that includesinformation describing the multi-terminal output with a common modeconnection 100 of FIG. 1, the driver 202 of FIG. 2, the resistor network300 of FIG. 3, the calibration block 400 of FIG. 4, the drivers 502,504, 506, and 508 of FIG. 5, or any combination thereof, in addition toother circuits or information. To illustrate, the data file may includeinformation corresponding to a system-on-chip (SOC) that includes themulti-terminal output with a common mode connection of FIG. 1, thedriver 202 of FIG. 2, the resistor network 300 of FIG. 3, thecalibration block 400 of FIG. 4, the drivers 502, 504, 506, and 508 ofFIG. 5, and that also includes additional electronic circuits andcomponents within the SOC.

The GDSII file 826 may be received at a fabrication process 828 tomanufacture the multi-terminal output with a common mode connection 100of FIG. 1, the driver 202 of FIG. 2, the resistor network 300 of FIG. 3,the calibration block 400 of FIG. 4, the drivers 502, 504, 506, and 508of FIG. 5, or any combination thereof, according to transformedinformation in the GDSII file 826. For example, a device manufactureprocess may include providing the GDSII file 826 to a mask manufacturer830 to create one or more masks, such as masks to be used withphotolithography processing, illustrated as a representative mask 832.The mask 832 may be used during the fabrication process to generate oneor more wafers 834, which may be tested and separated into dies, such asa representative die 836. The die 836 includes a circuit including adevice that includes the multi-terminal output with a common modeconnection of FIG. 1, the driver 202 of FIG. 2, the resistor network 300of FIG. 3, the calibration block 400 of FIG. 4, the drivers 502, 504,506, and 508 of FIG. 5, or any combination thereof.

The die 836 may be provided to a packaging process 838 where the die 836is incorporated into a representative package 840. For example, thepackage 840 may include the single die 836 or multiple dies, such as asystem-in-package (SiP) arrangement. The package 840 may be configuredto conform to one or more standards or specifications, such as JointElectron Device Engineering Council (JEDEC) standards.

Information regarding the package 840 may be distributed to variousproduct designers, such as via a component library stored at a computer846. The computer 846 may include a processor 848, such as one or moreprocessing cores, coupled to a memory 850. A printed circuit board (PCB)tool may be stored as processor executable instructions at the memory850 to process PCB design information 842 received from a user of thecomputer 846 via a user interface 844. The PCB design information 842may include physical positioning information of a packaged semiconductordevice on a circuit board, the packaged semiconductor devicecorresponding to the package 840 including the multi-terminal outputwith a common mode connection of FIG. 1, the driver 202 of FIG. 2, theresistor network 300 of FIG. 3, the calibration block 400 of FIG. 4, thedrivers 502, 504, 506, and 508 of FIG. 5, or any combination thereof.

The computer 846 may be configured to transform the PCB designinformation 842 to generate a data file, such as a GERBER file 852 withdata that includes physical positioning information of a packagedsemiconductor device on a circuit board, as well as layout of electricalconnections such as traces and vias, where the packaged semiconductordevice corresponds to the package 840 including the multi-terminaloutput with a common mode connection of FIG. 1, the driver 202 of FIG.2, the resistor network 300 of FIG. 3, the calibration block 400 of FIG.4, the drivers 502, 504, 506, and 508 of FIG. 5, or any combinationthereof. In other embodiments, the data file generated by thetransformed PCB design information may have a format other than a GERBERformat.

The GERBER file 852 may be received at a board assembly process 854 andused to create PCBs, such as a representative PCB 856, manufactured inaccordance with the design information stored within the GERBER file852. For example, the GERBER file 852 may be uploaded to one or moremachines to perform various steps of a PCB production process. The PCB856 may be populated with electronic components including the package840 to form a representative printed circuit assembly (PCA) 858.

The PCA 858 may be received at a product manufacture process 860 andintegrated into one or more electronic devices, such as a firstrepresentative electronic device 862 and a second representativeelectronic device 864. As an illustrative, non-limiting example, thefirst representative electronic device 862, the second representativeelectronic device 864, or both, may be selected from the group of a settop box, a music player, a video player, an entertainment unit, anavigation device, a communications device, a personal digital assistant(PDA), a fixed location data unit, and a computer, into which themulti-terminal output with a common mode connection of FIG. 1, thedriver 202 of FIG. 2, the resistor network 300 of FIG. 3, thecalibration block 400 of FIG. 4, the drivers 502, 504, 506, and 508 ofFIG. 5, or any combination thereof is integrated. As anotherillustrative, non-limiting example, one or more of the electronicdevices 862 and 864 may be remote units such as mobile phones, hand-heldpersonal communication systems (PCS) units, portable data units such aspersonal data assistants, global positioning system (GPS) enableddevices, navigation devices, fixed location data units such as meterreading equipment, or any other device that stores or retrieves data orcomputer instructions, or any combination thereof. Although FIG. 8illustrates remote units according to teachings of the disclosure, thedisclosure is not limited to these illustrated units. Embodiments of thedisclosure may be suitably employed in any device which includes activeintegrated circuitry including memory and on-chip circuitry.

A device that includes the multi-terminal output with a common modeconnection of FIG. 1, the driver 202 of FIG. 2, the resistor network 300of FIG. 3, the calibration block 400 of FIG. 4, the drivers 502, 504,506, and 508 of FIG. 5, or any combination thereof, may be fabricated,processed, and incorporated into an electronic device, as described inthe illustrative process 800. One or more aspects of the embodimentsdisclosed with respect to FIGS. 1-5 may be included at variousprocessing stages, such as within the library file 812, the GDSII file826, and the GERBER file 852, as well as stored at the memory 810 of theresearch computer 806, the memory 818 of the design computer 814, thememory 850 of the computer 846, the memory of one or more othercomputers or processors (not shown) used at the various stages, such asat the board assembly process 854, and also incorporated into one ormore other physical embodiments such as the mask 832, the die 836, thepackage 840, the PCA 858, other products such as prototype circuits ordevices (not shown), or any combination thereof. Although variousrepresentative stages of production from a physical device design to afinal product are depicted, in other embodiments fewer stages may beused or additional stages may be included. Similarly, the process 800may be performed by a single entity or by one or more entitiesperforming various stages of the process 800.

Those of skill would further appreciate that the various illustrativelogical blocks, configurations, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software executed by aprocessor, or combinations of both. Various illustrative components,blocks, configurations, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or processor executableinstructions depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in random access memory (RAM), flashmemory, read-only memory (ROM), programmable read-only memory (PROM),erasable programmable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), registers, hard disk, aremovable disk, a compact disc read-only memory (CD-ROM), or any otherform of non-transient storage medium known in the art. An exemplarystorage medium is coupled to the processor such that the processor canread information from, and write information to, the storage medium. Inthe alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in anapplication-specific integrated circuit (ASIC). The ASIC may reside in acomputing device or a user terminal. In the alternative, the processorand the storage medium may reside as discrete components in a computingdevice or user terminal.

The previous description of the disclosed embodiments is provided toenable a person skilled in the art to make or use the disclosedembodiments. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the principles defined hereinmay be applied to other embodiments without departing from the scope ofthe disclosure. Thus, the present disclosure is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope possible consistent with the principles and novel features asdefined by the following claims.

What is claimed is:
 1. A circuit comprising: an output element having afirst terminal and a second terminal and having a common mode connectionbetween the first terminal and the second terminal, wherein the outputelement is configured to apply a differential signal at the firstterminal and at the second terminal, and wherein the common modeconnection is configured to generate a common mode voltage of thedifferential signal; a first transistor having a bulk connection, thebulk connection coupled to the common mode connection, wherein the firsttransistor is coupled to the first terminal via a first resistor with afirst resistance; and a second transistor having the bulk connection,wherein the second transistor is coupled to the first terminal via asecond resistor with a second resistance, and wherein the secondresistance is greater than the first resistance.
 2. The circuit of claim1, further comprising a third transistor and a fourth transistor,wherein the first transistor is coupled to the first terminal andwherein the second transistor is coupled to the second terminal.
 3. Thecircuit of claim 2, wherein a first drain of the third transistor iscoupled to the first terminal, wherein a second drain of the fourthtransistor is coupled to the second terminal, wherein a first sourceterminal of the third transistor is coupled to a fifth transistor, andwherein a second source terminal of the fourth transistor is coupled toa sixth transistor.
 4. The circuit of claim 1, wherein the secondresistance is twice the first resistance.
 5. The circuit of claim 1,wherein the first transistor is a p-channel metal oxide semiconductor(PMOS) transistor.
 6. The circuit of claim 1, wherein multipletransistors are configured to control a resistive network that iscoupled to the first terminal and the second terminal.
 7. The circuit ofclaim 6, wherein a third transistor of the multiple transistors iscoupled to the first terminal via a third resistor of the resistivenetwork, wherein the third transistor of the multiple transistors iscoupled to the second terminal via a fourth resistor of the resistivenetwork, wherein a fourth transistor of the multiple transistors iscoupled to the first terminal via a fifth resistor of the resistivenetwork, and wherein the fourth transistor of the multiple transistorsis coupled to the second terminal via a sixth resistor of the resistivenetwork.
 8. The circuit of claim 1, wherein a first impedance controlsignal is provided to a first gate of the first transistor and wherein asecond impedance control signal is provided to a second gate of thesecond transistor.
 9. The circuit of claim 8, further comprisingimpedance control circuitry to generate the first impedance controlsignal and the second impedance control signal, wherein the firstimpedance control signal and the second impedance control signal have afirst rail voltage that is substantially the same as the common modevoltage of the common mode connection.
 10. The circuit of claim 9,wherein the first impedance control signal and the second impedancecontrol signal are generated by the impedance control circuitry based onlevel shifting control signals that have a second rail voltage that islower than the common mode voltage.
 11. The circuit of claim 1integrated in at least one semiconductor die.
 12. The circuit of claim1, further comprising a set top box, a music player, a video player, anentertainment unit, a navigation device, a communications device, apersonal digital assistant (PDA), a fixed location data unit, acomputer, or a combination thereof, into which the transistor isintegrated.
 13. An apparatus comprising: means for generating a commonmode voltage at a common mode connection, wherein the common modeconnection is between a first terminal and a second terminal, whereinthe means for generating is configured to apply a differential signal atthe first terminal and at the second terminal, and wherein the commonmode connection is configured to generate a common mode voltage of thedifferential signal; first means for adjusting an output impedance basedon a first input, the common mode voltage, and a first impedance betweenthe first means for adjusting the output impedance and the firstterminal; second means for adjusting the output impedance based on asecond input, the common mode voltage, and a second impedance betweenthe second means for adjusting the output impedance and the firstterminal, wherein the second impedance is greater than the firstimpedance.
 14. The apparatus of claim 13, further comprising means forproviding an output to the first terminal and the second terminal. 15.The apparatus of claim 13, wherein the means for adjusting the outputimpedance is within a high-definition multimedia interface (HDMI)compliant transmitter.
 16. A method comprising: receiving a data filecomprising design information corresponding to a semiconductor device;and fabricating the semiconductor device according to the designinformation, wherein the semiconductor device comprises: an outputelement having a first terminal and a second terminal and having acommon mode connection between the first terminal and the secondterminal, wherein the output element is configured to apply adifferential signal at the first terminal and at the second terminal,and wherein the common mode connection is configured to generate acommon mode voltage of the differential signal; a first transistorhaving a bulk connection, the bulk connection coupled to the common modeconnection, wherein the first transistor is coupled to the firstterminal via a first resistor with a first resistance; and a secondtransistor having the bulk connection, wherein the second transistor iscoupled to the first terminal via a second resistor with a secondresistance, and wherein the second resistance is greater than the firstresistance.
 17. The method of claim 16, wherein the data file has aGDSII format.
 18. The method of claim 16, wherein the data file has aGERBER format.
 19. The circuit of claim 1, wherein the common modeconnection is further configured to provide the common mode voltage tothe bulk connection.
 20. The circuit of claim 1, wherein the firstterminal comprises a first output terminal and the second terminalcomprises a second output terminal.
 21. The circuit of claim 8, whereinthe first gate of the first transistor is responsive to the firstimpedance control signal to adjust an output impedance of the outputelement based on an impedance of one or more transmission lines.
 22. Thecircuit of claim 8, further comprising impedance control circuitry tocalibrate impedance of the first transistor by generating the firstimpedance control signal.
 23. The circuit of claim 1, further comprisinga third transistor having a gate connection and a drain connection,wherein the common mode voltage is from a first power domain, whereinthe drain connection is coupled to the common mode connection, andwherein the gate connection is coupled to a supply voltage of a secondpower domain.
 24. The circuit of claim 1, wherein coupling of the commonmode connection to the bulk connection enables the transistor to operateat a higher voltage than an output voltage associated with the outputelement without reducing reliability of the transistor.
 25. Theapparatus of claim 13, wherein the common mode voltage varies based onthe differential signal.
 26. The apparatus of claim 13, wherein thecommon mode voltage is generated based on a power domain of a devicecoupled to the means for generating the common mode voltage.
 27. Theapparatus of claim 13, further comprising a third means for adjustingthe output impedance based on the common mode voltage and a supplyvoltage, wherein the common mode voltage is from a first power domain,and wherein the supply voltage is from a second power domain.
 28. Thecircuit of claim 1, wherein the first transistor is connected to thesecond terminal via a third resistor with the first resistance.
 29. Thecircuit of claim 28, wherein the second transistor is connected to thesecond terminal via a fourth resistor with the second resistance.
 30. Amethod comprising: generating a common mode voltage at a common modeconnection of an output element, wherein the common mode connection isbetween a first terminal and a second terminal, wherein the outputelement is configured to apply a differential signal at the firstterminal and at the second terminal, and wherein the common mode voltageis a common mode voltage of the differential signal; and adjusting anoutput resistance based on a first input of a first transistor receivingthe common mode voltage and a first resistance of a first resistorbetween the first transistor and the first terminal, wherein the outputresistance is further adjusted based on a second input of a secondtransistor receiving the common mode voltage and a second resistance ofa second resistor between the second transistor and the first terminal,wherein the second resistance is greater than the first resistance. 31.The method of claim 30, wherein the output resistance is furtheradjusted based on a third resistor with the first resistance, the thirdresistor between the first transistor and the second terminal.
 32. Anon-transitory computer readable medium storing instructions that whenexecuted cause a processor to perform operations comprising: fabricatinga semiconductor device, wherein the semiconductor device comprises: anoutput element having a first terminal and a second terminal and havinga common mode connection between the first terminal and the secondterminal, wherein the output element is configured to apply adifferential signal at the first terminal and at the second terminal,and wherein the common mode connection is configured to generate acommon mode voltage of the differential signal; a first transistorhaving a bulk connection, the bulk connection coupled to the common modeconnection, wherein the first transistor is coupled to the firstterminal via a first resistor with a first resistance; and a secondtransistor having the bulk connection, wherein the second transistor iscoupled to the first terminal via a second resistor with a secondresistance, and wherein the second resistance is greater than the firstresistance.
 33. The non-transitory computer readable medium of claim 32,wherein the first transistor is connected to the second terminal via athird resistor with the first resistance.
 34. A method comprising: afirst step for generating a common mode voltage at a common modeconnection of an output element, wherein the common mode connection isbetween a first terminal and a second terminal, wherein the outputelement is configured to apply a differential signal at the firstterminal and at the second terminal, and wherein the common mode voltageis a common mode voltage of the differential signal; a second step foradjusting an output resistance based on a first input of a firsttransistor receiving the common mode voltage and a first resistance of afirst resistor between the first transistor and the first terminal,wherein the output resistance is further adjusted based on a secondinput of a second transistor receiving the common mode voltage and asecond resistance of a second resistor between the second transistor andthe first terminal, wherein the second resistance is greater than thefirst resistance.
 35. The method of claim 34, wherein the outputresistance is further adjusted based on a third resistor with the firstresistance, the third resistor between the first transistor and thesecond terminal.